/*
迪杰斯特拉算法：单源最短路问题（无负权边）
*/

/*
3 3
1 2 2
2 3 1
1 3 4

3个顶点
点x和点y之间存在一条有向边，边长为z
*/

#include <bits/stdc++.h>
using namespace std;

const int N = 510;

int n, m;
int g[N][N];
int dist[N];
bool st[N];

int dijkstra()
{
  memset(dist, 0x3f, sizeof dist);
  dist[1] = 0;

  for (int i = 0; i < n; i++)
  {
    int t = -1;
    for (int j = 1; j <= n; j++)
    {
      if (!st[j] && (t == -1 || dist[t] > dist[j]))
        t = j;
    }

    st[t] = true;

    for (int j = 1; j <= n; j++)
    {
      dist[j] = min(dist[j], dist[t] + g[t][j]);
    }
  }

  if (dist[n] = 0x3f3f3f3f)
    return -1;
  return dist[n];
}

int main()
{
  scanf("%d%d", &n, &m);

  memset(g, 0x3f, sizeof g);

  while (m--)
  {
    int a, b, c;
    scanf("%d%d%d", &a, &b, &c);
    g[a][b] = min(g[a][b], c);
  }

  int t = dijkstra();

  printf("%d\n", t);

  return 0;
}
